None.
1. Field of the Invention
The present invention generally relates to the use of latches to hold jointed sections of manual pipe tongs as deployed in the oilfield industry together. More particularly, the invention relates to the addition of a secondary safety latch to a set of manual pipe tongs to prevent the undesired opening of the tong jaws.
2. Description of the Related Art
Manual pipe tongs are used throughout the oilfield industry to transmit torque to various tubular components of generally cylindrical shape. This assisted transmission of torque is most often used to secure, tighten (make-up), and loosen (break-out) the threaded connections of drill pipe, drill collars, casing, and tubing. Pipe tongs typically function by incorporating a cantilevered configuration that holds the workpiece in a grip that tightens as more torque is applied to the lever arm.
FIG. 1 shows a typical prior art manual tong assembly 10 as used in oilfield drilling operations to secure or rotate a generally cylindrical workpiece 12. This particular example of a manual tong assembly 10 includes a long jaw 14, a short jaw 16, a lug jaw 18, and a lever arm 20 all connected together at pivot points 22. A latch 24 is pinned to one end of the long jaw 14 and fits into a receiver step 26 at the end of the lug jaw 18.
FIGS. 2a and 2b show how different workpiece 12 sizes can be accommodated by adjusting the lengths and configurations of lug jaw 18. FIG. 2a shows a lug jaw 18 that includes an array of mounting locations 28 and a choice of receiver steps, 26 and 30, that may be used to adjust to various workpiece diameters (e.g. pipe diameters). Similarly, FIG. 2b details a hinged lug jaw 32 that is greater in length than lug jaw 18 and includes a hinged portion 34 attached to a lug portion 36 by means of a hinge 38 to allow even larger diameter workpieces to be accommodated by tong assembly 10.
Referring again to FIG. 1, jaws, 14, 16, and 18 are positioned around workpiece 12 and locked into place with latch 24. Each jaw may contain one or more sets of sharpened teeth 40 (tong dies) that are used to xe2x80x9cbitexe2x80x9d into workpiece 12 and prevent slippage when manual tong 10 is engaged. Once latch 24 is engaged, lever arm 20 can be rotated in direction xcex1 so that latch 24 is loaded in tension and tool 10 engages and applies torque to workpiece 12 in the xcex1 direction. Rotating lever arm 20 in direction xcfx89 will loosen jaw""s 14, 16, and 18 and allow latch 24 to be released. Several handles such as 42 and 44, are typically placed about the periphery of manual tong assembly 10 to provide locations for rig workers to guide tong assembly 10 during operations.
Manual tong 10, as illustrated, is configured to only grip workpiece 12 when torque is applied on the xcex1 direction. Typical rig operations incorporate two sets of manual tongs, with each one being the mirror image of the other, so that one tightens in clockwise direction and the other in a counter-clockwise direction. Each can tighten or loosen the pipe threads, depending on whether it is installed in the upper position for rotating the pin (male) connection or the lower position for holding the box (female) connection. The number of tongs used in an operation and their position on the workpiece relative to each other depends on the operation being performed and the type of additional rig equipment used.
It has been found that conventional tongs sometimes allow the undesired release of latch 24 when the tong is rotated in direction xcfx89. After workpiece 12 has been positioned, it sometimes becomes necessary to slidably rotate manual tong 10 backwards (counter-clockwise as drawn, in the xcfx89 direction) about workpiece 12, in a manner similar to a ratchet, so that the engagement and rotation steps can be repeated. Latch 24 of FIG. 1 is designed to engage when the manual tong device is loaded in direction xcex1. If the load applied in direction xcex1 were slackened, or if the tong is rotated in direction xcfx89, the latch device can release undesirably, allowing tong jaws 14, 16, and 18 to rotate and swing free of workpiece 12. Because jaws, 14, 16 and 18 are typically quite massive, such undesired openings can be hazardous, as well as requiring that operations cease until they are repositioned and secured. Any improvement made in latch 24 of manual tong 10 that is able to reduce such undesired openings would increase safety and reduce down-time and the costs associated therewith.
In addition, manual tong components occasionally work themselves loose during operations, which can cause the tong apparatus to open unexpectedly and rapidly. This undesired failure has great potential to cause physical harm to operators and nearby support personnel. This potential for injury can be greatly magnified if the tong is being operated under high loads at the time of the undesired opening. For this reason, a system that maintains the jaws in a closed configuration in the event of such a failure is highly desirable.
According to the present invention, the issues noted above are addressed by providing a latch device for a manual tong that incorporates a secondary catch mechanism. Such a secondary catch assists in maintaining the tong assembly in its closed position during a reversing operation or at a time when load applied to the manual tong device in the gripping direction is very low. Additionally the secondary catch provides protection from undesired release by holding some components of the tong assembly together in the event of a failure of certain tong components. The mechanism of the secondary catch is spring loaded and is deactivated by swinging a handle in a direction that corresponds to the operator""s natural motion to open the lug jaw.